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TitleConodonts from the Carnian-Norian boundary (Upper Triassic) of Black Bear Ridge, northeastern British Columbia, Canada
AuthorOrchard, M J
SourceGeological Society of America, Abstracts With Programs 2014.
Alt SeriesEarth Sciences Sector, Contribution Series 20140179
MeetingGeological Society of America Annual Meeting; Vancouver; CA; October 19-22, 2014
File formatpdf
ProvinceBritish Columbia
AreaBlack Bear Ridge; Williston Lake
Lat/Long WENS-123.5000 -123.0000 56.2500 56.0000
Subjectspaleontology; Upper Triassic; Carnian; Norian; conodonts; fossils; biostratigraphy; biochronology; Mesozoic; Triassic
ProgramWestern Arctic Sverdrup Basin, GEM2: Geo-mapping for Energy and Minerals
AbstractConodonts from the Carnian-Norian Boundary (CNB) interval at the Global Stratigraphic Section and Point (GSSP) candidate section at Black Bear Ridge (BBR), British Columbia, Canada, include five new genera (Acuminatella, Kraussodontus, Parapetella, Primatella, Quadralella), 75 new named taxa, 31 more in open nomenclature, and 43 new morphotypes. These elements and others display progressive morphogenesis through the strata of the Ludington and Pardonet formations, which represent a continuous Upper Triassic slope-basin succession developed at the western edge of Pangea.

Two conodont zones and nine subzones are defined for the interval, in ascending stratigraphic order: Carnepigondolella samueli Zone with the subzones of C. eozoae-Kraussodontus ludingtonensis; C. zoae; C. medioconstricta; and C. spenceri; the Primatella primitia Zone with the subzones of Acuminatella sagittale-Parapetella beattyi, A. angusta-Metapolygnathus dylani, A. acuminata-Pa. prominense, M. parvus (three subdivisions), and Primatella conservativa-Norigondolella sp. These strata are capped by the Early Norian Epigondolella quadrata Zone.

Conodont faunal turnovers are identified at the boundary between the samueli and primitia Zones, with the extinction of Carnepigondolella, and between the primitia and quadrata zones, with the extinction of Acuminatella and Primatella. The most significant turnover, however, is within the parvus Subzone where 58 taxa disappear, including all Quadralella, Kraussodontus, and most Parapetella species. The major decline and extinction is also marked by a bloom of diminutive taxa, and the ascendency of the Primatella stock. This turnover falls within a 5 m boundary interval lacking diagnostic ammonoids, but including the first occurrences of Halobia austriaca and Pterosirenites, favoured as Norian indicators, and also a carbon isotope minimum.

Conodont-ammonoid associations from the boundary interval elsewhere show that the entire ¿undated¿ boundary interval at BBR is equivalent to the Macrolobatus Zone. The disappearance of M. parvus and its diminutive associates at the top of the zone mark the closing of the Carnian chapter in conodont evolution, and correspond well to the traditional base of the Norian, i.e., base of the Kerri Zone.
Summary(Plain Language Summary, not published)
This presentation summarizes a monographic description of the conodonts from Black Bear Ridge in northeastern British Columbia, the proposed Global Stratigraphic Section and Point for the base of the Norian Stage of the Upper Triassic in the International Time Scale. Five new genera, 75 new named taxa, and as many others informally differentiated are introduced. Their evolutionary relationships and stratigraphic range enable the definition of nine new subzones, and several faunal turnovers, and their integration with other fossil indices provide options for boundary definition.